Fix convergence chart not recording first set of manual trials

Author: diegochine

client/src/probability-lab/engine/simulate-single.js

@@ -25,13 +25,16 @@ export default function simulateSingleTrials(stateSlice, rng, count) {
     stateSlice.trials += 1;
     stateSlice.lastIndex = idx;
     if (trialHistory) trialHistory.push(idx);
-  }
 
-  if (stateSlice.trials > 0) {
-    const rel = stateSlice.counts.map((c) => c / stateSlice.trials);
-    stateSlice.history.push({ trials: stateSlice.trials, rel });
-    if (stateSlice.history.length > 2000) {
-      stateSlice.history = stateSlice.history.filter((_, i) => i % 2 === 0);
+    // Record convergence snapshot after every trial
+    if (stateSlice.trials > 0) {
+      const rel = stateSlice.counts.map((c) => c / stateSlice.trials);
+      stateSlice.history.push({ trials: stateSlice.trials, rel });
     }
   }
+
+  // Decimate history if it exceeds 2000 entries (applied once after the loop)
+  while (stateSlice.history.length > 2000) {
+    stateSlice.history = stateSlice.history.filter((_, i) => i % 2 === 0);
+  }
 }

client/src/probability-lab/ui/charts/line-chart.js

@@ -73,8 +73,20 @@ export default function drawLineChart(canvas, xValues, yValues, theoryValue) {
     ctx.setLineDash([]);
     ctx.lineWidth = 1;
 
-    if (xValues.length < 2 || yValues.length < 2) return;
+    // Handle single data point case: draw a dot
+    if (xValues.length === 1 && yValues.length === 1) {
+      const x = maxX === 0 ? 0 : (xValues[0] / maxX) * plotW;
+      const y = (1 - clamp(yValues[0], 0, 1)) * plotH;
+      const px = padding.left + x;
+      const py = padding.top + y;
+      ctx.fillStyle = primary;
+      ctx.beginPath();
+      ctx.arc(px, py, 3, 0, Math.PI * 2);
+      ctx.fill();
+      return;
+    }
 
+    // Multiple data points: draw line with decimation
     const step = Math.max(1, Math.ceil(xValues.length / 500));
     ctx.strokeStyle = primary;
     ctx.lineWidth = 2;

tests/probability-lab/engine/simulate-single.test.js

@@ -125,6 +125,11 @@ describe('simulateSingleTrials', () => {
     expect(stateSlice.history.length).toBeLessThanOrEqual(2000);
   });
 
+  it('history is pruned below 2000 even for large batch counts', () => {
+    simulateSingleTrials(stateSlice, mockRng, 50000);
+    expect(stateSlice.history.length).toBeLessThanOrEqual(2000);
+  });
+
   it('maintains correct state across multiple calls', () => {
     simulateSingleTrials(stateSlice, mockRng, 3);
     const trialsAfterFirst = stateSlice.trials;